Investigation of a novel levitation technique for generation of solar grade silicon

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Solar energy is recognized as an important source of cleaner and inexhaustible energy. However, a shortage of raw materials with high purity and low cost restricts substantial development of this clean energy industry. The use of expensive raw material for the photovoltaic industry results in a high cost for photovoltaic electricity. Using relatively inexpensive metallurgical grade silicon (MG-Si) as a starting material for the production of solar grade silicon, is potentially one of the most economical ways to make solar cells. For example, solidification refining is an effective way to remove most of the impurities from molten silicon and does not require chemical processing. However phosphorus and boron are not removed by this technique. The novelty of the present proposal is to remove phosphorus from metallurgical grade silicon using a vacuum levitation technique. This method eliminates contamination of silicon by container materials and also avoids generation of hazardous industrial by-products. In order to achieve this goal, there are several short-term objectives: 1) Develop suitable induction coils to levitate and precisely control the temperature of molten silicon and silicon alloy droplets; 2) Measure thermodynamic data for phosphorus behaviour in the Si-P and Si-Fe-P systems; 3) Determine the kinetics of phosphorus removal from silicon and silicon alloy droplets; 4) Optimize conditions to accelerate phosphorus evaporation and limit silicon loss; and 5) Conduct a computer simulation to improve understanding of fluid flow, temperature distribution and mass and heat transfer within levitated droplets. A longer-term objective of the project is to provide highly qualified personnel with training suitable for employment in the critical areas of Materials Development, Environmental Studies and Solar Photovoltaic Engineering.